The present invention relates to a magnetic reproducing device for detecting a signal from a magnetic recording medium and, more particularly, to a device having an effective function against high-frequency range noise detected by a magnetic head.
With the recent increase of opportunities of using computers equipped with apparatus such as magnetic reproducing devices and so forth, there is developed an advanced contrivance of raising a clock frequency of a CPU (central processing unit) so as to process a greater quantity of information. And it is not unusual now to employ a CPU whose clock frequency is higher than 1 GHz.
Currently, popular computers are of a portable type ready to be carried with facility. In communication via an electric communication line, a portable computer uses a communication terminal such as a PHS (personal handyphone system) or a cellular phone. In any of these communication terminals, there is observed a trend of raising its clock frequency, and intense waves of higher than 1 GHz or so are used at present.
As described, any apparatus such as a magnetic reproducing device provided in a computer is kept exposed to severe environment with high-frequency high-energy electromagnetic noise.
Now a conventional magnetic reproducing device will be explained with reference to FIG. 7.
A magnetic reproducing device 2 comprises a magnetic head 30, a head amplifier 31 and a filter 32. The magnetic head 30 is connected to the head amplifier 31, and detects a magnetic signal from a magnetic recording medium, not shown, through access to a predetermined position of the recording medium. Then the head 30 converts the detected magnetic signal into a voltage value, and supplies the same to the head amplifier 31.
The magnetic head 30 employed here is an inductive head wherein a coil is wound around a magnetic core (of ferrite or the like) having a great magnetic permeability, and an air gap is formed in a portion corresponding to a magnetic face. The magnetic head 30 records information by residual magnetization caused by abrupt changes of a magnetic field when the magnetic recording medium is separated from the air gap. Further the magnetic head 30 reproduces the information by the electromotive force derived from the residual magnetism.
The head amplifier 31 is disposed between the magnetic head 30 and the filter 32. The head amplifier 31 amplifies the voltage value supplied from the magnetic head 30, and then supplies the amplified voltage value to the filter 32. The filter 32 is connected to the head amplifier 31, and has such a characteristic as to attenuate the noise of any frequency higher than the maximum reproduction frequency of the magnetic reproducing device 2. The filter 32 consists of a high pass filter, a low pass filter and a band pass filter. The high pass filter cuts off DC components and low frequencies unrequired for the reproduced signal; the low pass filter cuts off noise of high frequencies; and the band pass filter differentiates the waveform for detecting the peak of the reproduced signal. Lately, in magnetic recording media, the signal level of the magnetic signal is rendered lower for raising the recording density.
The magnetic reproducing device 2 is affected very sharply by the high-frequency high-energy electromagnetic noise. The high-frequency high-energy electromagnetic noise is transmitted via the magnetic head 30 to the signal processing circuit in the following stage. Since it is impossible to completely attenuate the high-frequency high-energy electromagnetic noise by the filter 32, such noise causes deterioration of the SN ratio relative to the internal signal in the magnetic reproducing device 2. As a result, there arises a problem that, in the magnetic reproducing device 2, some error may be generated at the time of detecting the magnetic signal from the magnetic recording medium.
In order to solve the known problem mentioned above, it has been customary heretofore to enclose the magnetic reproducing device 2 with an electromagnetic noise prevention shield.
For example, the electromagnetic noise prevention shield is formed by covering the magnetic reproducing device entirely with copper connected to zero volt, or by using a copper alloy or the like for composition of peripheral component parts around the magnetic head, such as a carriage, a magnetic head arm and a gimbal leaf spring. In another example, an aluminum plate is inserted between the circuit and the magnetic head, or leadwires and the periphery of the head amplifier are shielded with an aluminum plate.
However, the electromagnetic noise prevention shield needs to be composed of copper, aluminum or similar expensive material having a small electric resistance so as to cut off the high-frequency high-energy electromagnetic noise, hence bringing about another problem that the magnetic reproducing device is rendered expensive.
Further, particularly against high-frequency electromagnetic noise, there exist some technical difficulties since the electromagnetic noise prevention shield, is required to cover the whole magnetic reproducing device completely without any break. Moreover, in using a removable disk such as a floppy disk, it is difficult to perfectly cut off the high-frequency high-energy electromagnetic noise because a disk insertion slot is not coverable.
In addition to the above, there is another problem that, due to the use of a metallic material such as copper or aluminum, the electromagnetic noise prevention shield becomes heavier in weight and renders the apparatus inconvenient with regard to the portability thereof.